Question Number 126572 by sdfg last updated on 22/Dec/20
Answered by liberty last updated on 22/Dec/20
$$\:\mid\overset{\rightarrow} {{a}}+\overset{\rightarrow} {{b}}\mid^{\mathrm{2}} =\:\mid\overset{\rightarrow} {{a}}\mid^{\mathrm{2}} +\mid\overset{\rightarrow} {{b}}\mid^{\mathrm{2}} +\mathrm{2}\mid\overset{\rightarrow} {{a}}\mid\mid\overset{\rightarrow} {{b}}\mid\mathrm{cos}\:\alpha\: \\ $$$$\:\:\:\:\:\:\:\mathrm{50}\:\:\:\:=\:\mathrm{25}\:+\mathrm{25}\:+\:\mathrm{2}\left(\mathrm{5}\right)\left(\mathrm{5}\right)\mathrm{cos}\:\alpha \\ $$$$\:\:\:\:\:\:\:\mathrm{cos}\:\alpha\:=\:\mathrm{0}\:\rightarrow\:\alpha=\frac{\pi}{\mathrm{2}} \\ $$